The present invention relates to a high-pressure discharge lamp lighting apparatus for lighting a high-pressure discharge lamp with a high-frequency AC voltage. Moreover, the present invention relates to a luminaire using such a high-pressure discharge lamp lighting apparatus.
Generally, a discharge lamp lighting apparatus is provided with an inverter circuit and an LC resonance circuit. At the time of starting a discharge lamp, a high frequency AC voltage is initially applied from the inverter circuit to the discharge lamp through the LC resonance circuit. The frequency of the AC voltage is then gradually lowered close to a resonance frequency of the LC resonance circuit. Thereby, the output voltage of the LC resonance circuit rises. As the output voltage of the LC resonance circuit reaching a glow discharge of the discharge lamp, the glow discharge is started. After the operation of the high-intensity discharge lamp has transferred from the glow discharge to an arc discharge, an arc-spot generates on a main portion of the electrode. Then, the discharge lamp is lit up. After the discharge lamp has been lit up, the frequency of the inverter circuit is further lowered so as that the discharge lamp is steadily lit up at a frequency not involving acoustic resonance in the discharge lamp.
On the other hand, the applied voltage must be kept high for a predetermined time to ensure the glow discharge to arc discharge transition of the high-pressure discharge lamp. A prior art, JP2000-58284-A, discloses"" a ballast having a booster circuit provided in preceding the inverter circuit. In a starting operation, the booster circuit boosts up the applied voltage higher than the steady lighting voltage for starting the operation of the high-pressure discharge lamp.
There exists an astable operation window, i.e., a frequency range where acoustic resonance occur in the high-pressure discharge lamp. Thereby, at the time of starting as well as in the steady lighting, a frequency in a stable operation window, i.e., a frequency range where acoustic resonance never occur in the high-pressure discharge lamp. The resonance frequency of the LC resonance circuit is set up in the stable operation window in the vicinity of or higher than the steady lighting frequency.
In this prior art, since the glow discharge causing frequency, a glow discharge to arc discharge transition causing frequency, and the steady lighting frequency reside in the stable operation window, acoustic resonance never occurs.
However, in such frequencies load characteristics of the half-bridge type inverter circuit has a stable current characteristics of generating almost constant current independently from load impedances. Moreover, when the lamp voltage varies, the lamp operating power changes extensively. Furthermore, the lamp operating power extensively changes in accordance with a frequency change. Therefore, the lamp operating power varies extensively even if a frequency slightly shifts according to a change of ambient temperature around the inverter control circuit. In the high-pressure discharge lamp, there is also a problem that a color temperature changes according to the change of the lamp operating power. Consequently, the lamp operating power is expected to be controlled to have a constant value. However, for that purpose, the high-pressure discharge lamp lighting apparatus is upsized and becomes expensive.
Furthermore, in case of switching the output voltage of the booster circuit JP2000-58284-A, the inverter control circuit becomes complicated. Furthermore, since the output voltage of the booster circuit is raised higher than the voltage in the steady lighting operation, more large-sized high electric strength components are required, and the high-pressure discharge lamp lighting apparatus is upsized. Particularly, in the high-pressure discharge lamp using a small-size bulb base, it is desirable for preventing a breakdown at the bulb base that the starting voltage generated by this high-pressure discharge lamp lighting apparatus is lowered whenever possible and that the amplitude of the starting voltage generated in every starting operation has little dispersion for every starting operation.
It is an object of the invention to provide a discharge lamp lighting apparatus with a little change in its lamp power to a change of a lamp voltage, and little dispersion in its starting voltage for every starting operation.
AD first aspect of the high-pressure discharge lamp lighting apparatus according to the present invention, comprises an LC resonance circuit, wherein the LC resonance circuit has a resonance frequency set up in two to three times the steady lighting frequency of the high-pressure discharge lamp, and the LC resonance circuit is connected to the high-pressure discharge lamp; a DC power source; an inverter circuit, wherein the inverter circuit has an input terminal connected to the DC power source, and an output terminal connected to the high-pressure discharge lamp through the LC resonance circuit, and the inverter circuit converts the DC power of the DC power source into an AC power, and causes to start and steadily operate the high-pressure discharge lamp; and an inverter control circuit, wherein the inverter control circuit is connected to a control terminal of the inverter circuit, the inverter control circuit operates the inverter circuit at a frequency around or higher than the resonance frequency of the LC resonance circuit at the time of starting the operation of the high-pressure discharge lamp, and the inverter control circuit operates the inverter circuit at a frequency in a range lower than the resonance frequency of the LC resonance circuit and free from acoustic resonance in the steady lighting operation of the high-pressure discharge lamp.
In this application, some terms are defined to have the following technical meanings, unless otherwise specified.
The term xe2x80x9chigh-pressure discharge lampxe2x80x9d means a mercury lamp, a metal halide lamp, a high-pressure sodium lamp, etc. The term xe2x80x9chigh-pressure discharge lampxe2x80x9d also admits a ceramic discharge lamp which uses an alumina for the arc tube. The arc tube is filled with at least rare gas, such as Neon (Ne), Argon (Ar), etc, as discharge agent.
The inverter circuit has, for example, a half-bridge type configuration by using two switching elements. These two switching elements alternately switch ON and OFF a DC power source so that the high-frequency AC voltage is obtained on the output side of the inverter circuit. An LC resonance circuit is connected to the output side of the inverter circuit. The resonance frequency of the LC resonance circuit is adjusted to the steady lighting frequency of the high-pressure discharge lamp. By the way, the inverter circuit may be a single-transistor type or a four-transistor type configuration.
The LC resonance circuit outputs the AC voltage at a high output rate, when the frequency of the high-frequency AC voltage applied from the inverter circuit is close to the resonance frequency. The inverter circuit is set up so that it may operate at a frequency in two to three times the resonance frequency of the LC resonance circuit at the time of starting the operation of the high-pressure discharge lamp. Thereby, the inverter circuit can steadily operate the high-pressure discharge lamp at an operating point voltage thereat the load power becomes almost maximum. The inverter circuit can prevent that the inverter circuit oscillates at an advancing phase. Therefore, a switching loss of the inverter circuit is restricted.
An inverter control circuit controls the inverter to oscillate at a frequency around or higher than the resonance frequency of the LC resonance circuit at the time of starting the operation of the high-pressure discharge lamp. And after the high-pressure discharge lamp has lit up, the inverter control circuit controls the inverter circuit to oscillate at a frequency lower than the resonance frequency of the LC resonance circuit and not causing acoustic resonance.
According to this aspect of the high-pressure discharge lamp lighting apparatus, the high-pressure discharge lamp is steadily lit up at the frequency not causing acoustic resonance and where the load power of the high-pressure discharge lamp becomes to maximum. Therefore, acoustic resonance never occurs, and even if the lamp voltage has changed, a rapid fluctuation of a load power of the high-pressure discharge lamp is restricted. The frequency is kept constant during the steady lighting operation of the high-pressure discharge lamp. Thereby, an abnormal high voltage is not generated at the lamp-life terminal.
A second aspect of the high-pressure discharge lamp lighting apparatus according to the present invention, comprises an LC resonance circuit, wherein the LC resonance circuit has a resonance frequency set up in two to three times the steady lighting frequency of the high-pressure discharge lamp, and the LC resonance circuit is connected to the high-pressure discharge lamp; a DC power source; an inverter circuit, wherein the inverter circuit having an input terminal where the inverter circuit was connected to the DC power source, and an output terminal connected to the high-pressure discharge lamp through the LC resonance circuit, and the inverter circuit converts the DC power of the DC power source into an AC power, and causes to start and steadily operate the high-pressure discharge lamp; and an inverter control circuit, wherein the inverter control circuit is connected to control terminal of the inverter circuit, the inverter circuit operates the inverter control circuit for a predetermined time from the time of starting the operation of the high-pressure discharge lamp at a frequency around or higher than the resonance frequency of the LC resonance circuit, and the inverter control circuit operates the inverter circuit at a frequency in a range lower than the resonance frequency of the LC resonance circuit and free from acoustic resonance in the steady lighting operation of the high-pressure discharge lamp.
The second aspect of the high-pressure discharge lamp lighting apparatus is characterized by that the inverter circuit operates at a frequency higher than frequency at the time of the steady lighting for a prescribed time from the time of starting the operation of the high-pressure discharge lamp.
The high-pressure discharge lamp has a property that a glow discharge occurs initially and then the discharge lamp is lit up at the time the glow discharge has transferred to an arc discharge. Consequently, at the time of starting, for a predetermined time after the time of starting the inverter circuit are operated at the frequency higher than a frequency in the steady lighting operation of the high-pressure discharge lamp, thereby the glow discharge to arc discharge transition is ensured.
For example, an inverter control circuit applies a frequency about four times the high frequency of the steady lighting to the inverter circuit at the time of starting. Then, the frequency of the AC voltage is lowered gradually. Then, in the meantime the glow discharge occurs around the electrodes of the high-pressure discharge lamp. And the frequency of the AC voltage is further lowered to the vicinity of the resonance frequency of the LC resonance circuit. And it is maintained at a frequency around or higher than the resonance frequency. In the meantime, a glow discharge to arc discharge transition is ensured in the high-pressure discharge lamp, and thus the high-pressure discharge lamp is lit up.
According to a second aspect of the high-pressure discharge lamp lighting apparatus, a glow discharge to arc discharge transition is ensured in the high-pressure discharge lamp. Therefore, the high-pressure discharge lamp can be surely lit up.
A third aspect of the high-pressure discharge lamp lighting apparatus according to the present invention is characterized by that when the high-pressure discharge lamp is that filled with Neon and Argon, the predetermined time is set up in 1-10 seconds.
While, a fourth aspect of the high-pressure discharge lamp lighting apparatus according to the present invention is characterized by that when the high-pressure discharge lamp is that filled with only Argon, the predetermined time is set up in 0.1-1.5 seconds.
The glow discharge to arc discharge transition time differs in accordance with the type of the rare gas filled in the high-pressure discharge lamp. Thereby, the third aspect of the high-pressure discharge lamp lighting apparatus sets up the predetermined time appropriately according to the type of the rare gas. According to the third and fourth aspects of the high-pressure discharge lamp lighting apparatus, a glow discharge to arc discharge transition can be executed appropriately in response to the type of rare gas filled in the high-pressure discharge lamp.
A fifth aspect of the high-pressure discharge lamp lighting apparatus according to the present invention, further comprises a starting control circuit, wherein the starting control circuit judges whether the high-pressure discharge lamp is in non-lighting state, and when it is judged that the high-pressure discharge lamp is in non-lighting state, the starting control circuit intermittently operates the inverter control circuit.
A starting control circuit has the lamp voltage detection circuit which detects the lamp voltage of the high-pressure discharge lamp, the oscillation halting circuit which stops the oscillation of an inverter control circuit when abnormal lamp voltage is detected in the lamp voltage detection circuit, and the timer circuit which counts the time after the starting control operation of the starting control circuit begins. And if an abnormal lamp voltage is detected, it is judged with the high-pressure discharge lamp being in non-lighting state. In the case, the starting control circuit controls the starting and the steadily lighting of the high-pressure discharge lamp 12 are intermittently executed at an interval of a predetermined time.
According to the fifth aspect of the high-pressure discharge lamp lighting apparatus a high voltage required for starting and steadily lighting up the discharge lamp is intermittently applied when the high-pressure discharge lamp is in a non-lighting state. Thus it can be prevented that the high voltage is continuously applied to the high-pressure discharge lamp.
A sixth aspect of the high-pressure discharge lamp lighting apparatus according to the present invention, further comprises a booster circuit, wherein the booster circuit is connected between the DC power supplies and the inverter circuits, the booster circuit keeps the DC voltage applied in the inverter circuit constant, and at the time of starting the operation of the high-pressure discharge lamp, the inverter control circuit controls the inverter circuit so that the output current of the LC resonance circuit becomes fixed.
The booster circuit is connected to the input side of the inverter circuit. Thereby, the DC voltage applied to the inverter circuit is kept constant. An inverter control circuit controls the starting voltage to have less dispersion in every starting operation by feeding back the resonance current of the LC resonance circuit and controlling the oscillation frequency so as that the resonance current of the LC resonance circuit becomes constant at the time of starting the operation of the high-pressure discharge lamp in every starting operation. Thereby, the starting voltage is made to have less dispersion in every starting operations.
According to the sixth aspect of the high-pressure discharge lamp lighting apparatus, the DC voltage of the booster circuit applied to the inverter circuit is controlled equivalently. Consequently, as the current supplied to the LC resonance circuit is controlled to be kept constant, the starting voltage of the LC resonance circuit is controlled in constant. Therefore, the amplitude of the starting voltage applied to the high-pressure discharge lamp becomes almost the same amplitude in every starting operation. Thereby the dispersion of the high-pressure discharge lamp in every starting operation is decreased. Therefore, it becomes possible to miniaturize the bulb base of the high-pressure discharge lamp, and the luminaire using the high-pressure discharge lamp and the high-pressure discharge lamp can be miniaturized.
A seventh aspect of the high-pressure discharge lamp lighting apparatus according to the present invention, is characterized by that when the intermittent starting control of the starting control circuit has continued for a predetermined time, at least the inverter control circuit halts.
In the seventh aspect of the high-pressure discharge lamp lighting apparatus, a starting control circuit has the lamp voltage detection circuit which detects the lamp voltage of the high-pressure discharge lamp, the oscillation halting circuit which halts the oscillation of an inverter control circuit when abnormal lamp voltage is detected in the lamp voltage detection circuit, and the timer circuit which counts the time after the starting control operation of the starting control circuit has started. And if an abnormal lamp voltage is detected, it is judged with the high-pressure discharge lamp being in non-lighting state. In the case, the starting control circuit controls the starting and the steadily lighting of the high-pressure discharge lamp 12 are intermittently executed at an interval of a predetermined time. And when the intermittent starting control has continued for a predetermined time, at least the inverter control circuit is halted.
High-pressure discharge lamps have an attribute that after a long term of extinction the glow discharge starting voltage stays in low, while immediately after a extinction the glow discharge starting voltage stays in high. Then, when the high-pressure discharge lamp fails to be lit up even if the starting operation has been continued for a predetermined time, at least the inverter control circuit is halted. And thus the inverter circuit is also halted.
According to the seventh aspect of the high-pressure discharge lamp lighting apparatus, when the high-pressure discharge lamp fails to be lit up within a predetermined time, at least the inverter control circuit is halted. Therefore, it is prevented that the starting voltage is wastefully applied to the discharge lamp for a long time repeatedly. Therefore, a high-pressure discharge lamp getting old over its lifetime can be safely exchanged.
A luminaire according to further aspect of the present invention, comprises the high-pressure discharge lamp lighting apparatus as claimed in any one of claims 1 to 7; and a main body capable of equipping the high-pressure discharge lamp operable with the high-pressure discharge lamp lighting apparatus.
According to the further aspect of the present invention, the luminaire is also able to have the effects obtained in the first to seventh aspects of the high-pressure discharge lamp lighting apparatus.